The mathematic expression for scattering cross section in inhomogeneous material is deduced in this paper. Then, the quantization of Kramers Kronig relation in inhomogeneous medium containing scatterers and non chatterers is given.Based on the frequency change,the phase velocity due to the inhomogeneous material is introduced into two dimensional Kirchhoff approximation formula.Finally,the flaw shapes in inhomogeneous medium is reconstructed by using backscattered ultrasound through experimental method.The results verify the feasibility of flaw scattering theory.